A variety of parallel optical communications devices exist for simultaneously transmitting and/or receiving multiple optical data signals over multiple respective optical data channels. Parallel optical transmitters have multiple optical transmit channels for transmitting multiple respective optical data signals simultaneously over multiple respective optical waveguides (e.g., optical fibers). Parallel optical receivers have multiple optical receive channels for receiving multiple respective optical data signals simultaneously over multiple respective optical waveguides (e.g., optical fibers). Parallel optical transceivers have multiple optical transmit channels and multiple optical receive channels for transmitting and receiving multiple respective optical transmit and receive data signals simultaneously over multiple respective transmit and receive optical waveguides (e.g., optical fibers).
For each of these different types of parallel optical communications devices, a variety of different designs and configurations exist. A typical layout for a parallel optical communications device includes a flex circuit on which a plurality of active optical devices (e.g., laser diodes and/or photodiodes) are mounted and a circuit board, such as a printed circuit board (PCB), a ball grid array (BGA), or the like, that is electrically connected to the flex circuit. In the case of a parallel optical transmitter, in addition to the laser diodes that are mounted to the flex circuit, a laser diode driver integrated circuit (IC) is typically also mounted on the flex circuit. The flex circuit has electrical conductors running through it that are electrically connected to electrical contact pads of the laser diodes and of the laser diode driver IC. The circuit board to which the flex circuit is electrically connected also has electrical conductors running through it (i.e., electrical traces and vias) and electrical contact pads on it. Through the electrical connections between the flex circuit and the circuit board, the electrical contact pads of the laser diode driver IC are electrically connected to the electrical conductors of the circuit board. One or more electrical components, such as a controller IC and other electrical components, are typically mounted on and electrically connected to the circuit board, thereby providing electrical connections between one or more of these electrical components and the laser diode driver IC mounted on the flex circuit. The flex circuit of the typical parallel optical transmitter often has additional components mounted thereon, such as, for example, monitor photodiodes and associated circuitry for monitoring and adjusting the output power levels of the laser diodes.
Similar configurations are used for parallel optical receivers, except that the flex circuit of a parallel optical receiver has a plurality of photodiodes instead of laser diodes and a receiver IC instead of a laser diode driver IC mounted on it. Parallel optical transceivers typically have laser diodes, photodiodes, a laser driver diode IC, and a receiver IC mounted on the flex circuit, although one or more of these devices may be integrated into the same IC to reduce part count and to provide other benefits.
In the aforementioned parallel optical communications devices, the circuit board (e.g., a BGA) of the device typically has a heat sink device mounted on the upper surface thereof. The controller IC is typically attached by a thermally conductive material to this heat sink device to enable heat generated by the controller IC to pass into and be dissipated by the heat sink device. The portion of the flex circuit on which the laser diode driver IC or receiver IC are mounted typically is in contact with one or more other heat sink devices that dissipate heat produced by these ICs.
The aforementioned heat sink devices have various shapes or configurations, but have the same general purpose of receiving heat generated by the ICs and absorbing and/or spreading out the heat such that the heat is moved away from the ICs. Heat generated by the ICs can detrimentally affect the performance of the parallel optical communications device. For example, in parallel optical transmitters and transceivers, the laser diode driver ICs generate large amounts of heat. If adequate measures to dissipate this heat are not taken, the heat can detrimentally affect the performance of the laser diode ICs, which are typically placed in relatively close proximity to the laser diode driver IC. Heat dissipation considerations are even more important in parallel optical communications device due to the large number of channels and associated electrical circuitry.
In addition to being effective at dissipating heat, heat sink devices should be efficient in terms of space utilization. Also, because heat sink devices are typically made of an electrically conductive material, such as copper, for example, they can affect the electromagnetic characteristics of the optical communications device. This is especially true in parallel optical communications devices due to the relatively large number of high speed signals that are carried on the electrical conductors of the flex circuit and the circuit board. If the heat sink device is too close to these high speed signal pathways, it can create capacitances that degrade signal quality. Therefore, heat sink devices should also be designed in ways that do not degrade signal quality.
There is an ever-increasing need to decrease the size of parallel optical communications devices and to increase the number of channels of parallel optical communications devices. In order to meet these needs, the layout of a parallel optical communications device should be efficient in terms of space utilization, have highly effective heat dissipation characteristics, and protect signal integrity. Accordingly, a need exists for a parallel optical communications device that achieves these goals.